type: Hooke

references:
  - R.A. Ayres et al.,
    Journal of Applied Physics 46:1526-1530, 1975,
    https://doi.org/10.1063/1.321804,
    fit to Table IV (T_min=100K, T_max=300K)

C_11: 535.1e+9
C_11,T: -6.459e+07
C_11,T^2: -1.664e+05

C_12: 216.1e+9
C_12,T: 2.357e+07
C_12,T^2: 5.186e+04

C_44: 161.1e+9
C_44,T: -1.498e+07
C_44,T^2: -3.234e+04

T_ref: 293.15